In a substrate-related-operation performing apparatus such as an electronic-circuit-component mounting apparatus that mounts an electronic-circuit component on a circuit substrate, if a current sort of circuit substrates are changed to a new sort of circuit substrates, it is often desirable to change at least one constituent portion of the apparatus. To this end, the apparatus includes at least one constituent element that is detachably attached thereto, and the current constituent element corresponding to the current sort of circuit substrates is exchanged with another constituent element corresponding to the new sort of circuit substrates. An example of the electronic-circuit-component mounting apparatus is disclosed by Japanese Patent Application Publication No. 8-46392. The disclosed apparatus includes a rotatable body that is intermittently rotatable about an axis line; and a plurality of nozzle holding portions that are supported by an outer portion of the rotatable body, such that the nozzle holding portions are equidistantly spaced from each other, and that hold a plurality of suction nozzles, respectively, each of which holds, by suction, an electronic-circuit component. Thus, the respective components held by the suction nozzles are intermittently revolved about the above-indicated axis line. In this electronic-circuit-component mounting apparatus, first, an operator detaches, from the nozzle holding portions, one or more suction nozzles that are not needed to mount electronic-circuit components on the next sort of circuit substrates, and additionally places a nozzle stocker holding a plurality of suction nozzles, on an X-Y table. Subsequently, as the rotatable body is intermittently rotated, each of the nozzle holding portions is sequentially positioned at a predetermined angular phase, while the X-Y table moves the nozzle stocker so as to position one of the suction nozzles held thereby, at a position right below an empty one of the nozzle holding portions. In this state, when the empty nozzle holder portion is lowered, the one suction nozzle is attached to the nozzle holding portion.